Contra-rotating compressors



April 23, 6 M. R. GARNIER 3,379,366

CONTRA-ROTAT ING COMPRESSORS Filed Nov. 16, 1966 am (w Mag 4 uhlDw Unitd States Patent 3,379,366 CONTRA-ROTATING COMPRESSORS Michel RobertGarnier, Sceaux, Hauts-de-Seine, France,

assignor to Socicte Nationals dEtude et de (Zonstruction de MoteursdAviation, Paris, France, a company of France Filed Nov. 16, 1966, Ser.No. 594,935 Claims priority, application aFrance, Nov, 18, 1965,

3 Claims. 51330-415 This invention relates to a multiple-stagecompressor of the type comprising two contra-rotating coaxial rotors theblades of which are arranged alternately in sequence.

In multiple stage compressors the general principle is known thatcorrect adjustment can be achieved and operating stability improved atlow engine speeds by opening one or more flap valves arranged radiallyof one or more stages of the compressor. The flap valves discharge aproportion of the air flow to atmosphere, thereby relieving the engineand preventing surging and consequent stalling of the engine.

The construction and positioning of the flap valves do not present anyspecial problems in the case of conventional compressors with a fixedstator, the latter being readily adaptable to include such valves.

However, in the case of contra-rotating compressors, no stator (as such)is provided, both sets of blades being rotatable with one set having theblade roots radially innermost and the other set having the blade rootsradially outermost so that the two sets of blades are respectivelydriven through the inner and outer peripheries thereof. In the case ofthe set of blades having the blade roots outermost a rotatable drum isused to the inner surface of which the blades are attached.

In accordance with the present invention, the rotatable drum is enclosedby a fixed outer casing, ports being provided in the rotatable drumradially of one or more stages of the compressor, and at least oneaperture being arranged in the casing radially of the ports and beingassociated with a flap valve or similar discharge unit, controlledmanually or automatically, the intervening annular space between therotatable drum and the fixed casing being in communication with theports, and/or each aperture lying between axially spaced seals, orexample labyrinth seals.

The invention will now be further described with reference to theaccompanying drawing which shows, by way of example, a contra-rotatingcompressor in accordance with the invention, the drawing being a scrapview in axial half-section.

One rotor of the contra-rotating compressor comprises a set of blades 1each of which is attached at the root to the inner surface of arotatable drum 3 in such manner that the blades extend generallyradially inwardly and are disposed in a series of radial planes. Thedrum 3 is coupled to a shaft 4 rotatably mounted in bearings 5 so thatin use rotation of the shaft 4 in one direction causes correspondingrotation of the drum 3 carrying the blades 1. A second shaft 6, coaxialwith the shaft 4, is rotatably mounted in bearings 7 and is coupled to asecond rotor comprising a set of blades 2 which, in use, rotate in theopposite direction to the blades 1. A forward bearing 8 is provided forthe rotor 3. The contra-rotating compressor constituted in this manneris preceded by a guide vane arrangement 9 at the intake to which theforward fairing 10 is attached and which is followed by an outlet 'iceguide vane arrangement 11 leading to a combustion chamber 12 of anengine supplied by the compressor. The complete structure is enclosed bya fixed casing 13.

In accordance with the present invention, circumferentially spaced ports14 are provided in the rotatable drum 3 radially of one of thecompressor stages. An aperture 15 is arranged in the casing 13 radiallyof the ports 14,

this aperture being in controlled communication with the surroundingatmosphere through a duct 16 in which is mounted a discharge valve 17controlled manually or antomatically. The intervening annular space 18between the rotatable drum 3 and the fixed casing 13 is in communicationwith the ports 14 of the drum and with the aperture 15 of the casing andis closed longitudinally by axially spaced labyrinth seals 19, 20attached to the casing 13 so that the aperture 15 lies between them inthe axial direction. The seals 19, 20 prevent the escape of air betweenthe rotatable drum 3 and the fixed casing 13.

Some of the air from the selected stage flows, under the influence ofcentrifugal force, through the ports 14 which, as the drum 3 rotates,are successively in radial alignment with the fixed aperture 15. The airbled off in this manner escapes to the surrounding atmosphere accordingto the extent to which the valve 17 is open, the air being at a positivegauge pressure with respect to the atmosphere.

In this way the present invention enables the acceptable operationalrange of contra-rotating compressors to be extended beyond thetheoretical limit by improving stability at low engine speeds; this isachieved by the provision of one or more discharge valves 17 operatedmanually or automatically and communicating with one or more apertures15 arranged on the fixed outer casing 13 and located substantially inthe same radial plane as the ports 14 in the rotating drum 3 of thecompressor and in the same radial plane as the bleed-off stage.

What is claimed is:

1. A contra-rotating compressor comprising two rotors each with a set ofblades, the set of blades of one rotor being attached to the innersurface of a rotatable drum, means to cause the two sets of blades torevolve in opposite directions, a fixed outer casing enclosing theretatable drum, said drum including ports formed in the surface thereofin a radial plane containing at least one compressor stage, said casinghaving an aperture, the ports being radially aligned with the aperturein the casing, means for connecting the aperture to the surroundingatmosphere, and sealing means between the rotatable drum and the fixedcasing on each axial side of the aperture.

2. A contra-rotating compressor according to claim 1, wherein saidsealing means are constituted by labyrinth seals.

3. A contra-rotating compressor according to claim 2, wherein the meansfor connecting the aperture to the atmosphere comprise a duct providedwith a discharge valve. T

References Cited UNITED STATES PATENTS 2,451,944 10/1948 Hall 230123FOREIGN PATENTS 268,903 4/1927 Great Britain.

25,756 5/1906 Sweden.

HENRY F. RADUAZO, Primary Examiner.

1. A CONTRA-ROTATING COMPRESSOR COMPRISING TWO ROTORS EACH WITH A SET OFBLADES, THE SET OF BLADES OF ONE ROTOR BEING ATTACHED TO THE INNERSURFACE OF A ROTATABLE DRUM, MEANS TO CAUSE THE TWO SETS OF BLADES TOREVOLVE IN OPPOSITE DIRECTIONS, A FIXED OUTER CASING ENCLOSING THEROTATABLE DRUM, SAID DRUM INCLUDING PORTS FORMED IN THE SURFACE THEREOFIN A RADIAL PLANE CONTAINING AT LEAST ONE COMPRESSOR STAGE, SAID CASINGHAVING AN APERTURE, THE PORTS BEING RADIALLY ALIGNED WITH THE APERTUREIN THE CASING, MEANS FOR CONNECTING THE APERTURE TO THE SURROUNDINGATMOSPHERE, AND SEALING MEANS BETWEEN THE ROTATABLE DRUM AND THE FIXEDCASING ON EACH AXIAL SIDE OF THE APERTURE.